In order to produce waterproof footwear, footwear is manufactured totally from rubber or another polymer through a dipping or molding technique, such that there is no separation between the upper and the outer sole, and therefore the footwear is water-impermeable. However, waterproof footwear produced through a dipping or molding technique has poor fit, is heavy in weight, and is impermeable to water vapor. Additionally, waterproof footwear produced through a dipping or molding technique is not readily adaptable to various footwear styles.
In recent times, footwear was manufactured whose body or upper part consists of water-impermeable, and preferably, water vapor-permeable material. There have been problems in providing a waterproof connection between the upper and an outer sole of the footwear while still maintaining the good fit, lightweight, and water vapor-permeable quality of the upper material.
In an attempt to produce waterproof footwear whose upper part consists of water-impermeable and water vapor-permeable material, a cement process of lasting footwear was developed. In this process, an upper of a shoe is cemented to an insole. To this unit, a sole is applied which may be an intermediate sole or an outer sole. It is a problem to have truly waterproof footwear with cement-lasted footwear, even if a water-impermeable outer sole and a water-impermeable upper layer are utilized in the construction. The weak point in the production of waterproof cement-lasted footwear is the formation of a durable waterproof seal between the insole and the upper since the lasting cement does not initially seal between the upper and the insole and may become brittle and more water-permeable due to bending stresses during use of the footwear. The formation of a durable waterproof seal between the insole and the upper is hampered in the lasting process since pleats form in the edges of the upper materials because the straight edges of the upper are forced to lay flat against the curved insole. These upper wrinkles are three-dimensional in nature and therefore provide easy routes for water entry into the upper of the footwear.
To overcome problems with the cement process of lasting footwear, a waterproof insert method was developed wherein a unit of a footwear upper and a cemented insole is lined with a sock-like insert of a water impermeable, water vapor-permeable material, as taught in U.S. Pat. No. 4,599,810, to Sacre. To obtain an insert that is waterproof and of the desired shape, the insert must first be sewn and then hot-welded at the sewn seams to form a waterproof article. This waterproof insert method does not allow the insole to be directly attached to a shoe last in a single step as in the traditional cement process of lasting footwear. An additional lasting step is usually required by this method, making this method more complicated and expensive for most shoe manufacturers.
An injection molding process for the soling of footwear, as taught in U.S. Pat. No. 4,899,465 to Bleimhofer, et al., has been used to produce waterproof footwear. A polyurethane outer sole is molded by machine to the sole region of an upper. It is necessary to have an injection mold that is applied to the upper from both sides. This injection mold is relatively expensive. Due to the high mold costs, the shoe manufacturers are restricted to very few sole configurations. Besides, it is not possible to achieve footwear having an elegant appearance with such molded-on outer soles.
The instant invention is directed to an improvement of the cement process of lasting footwear in such a manner that the connection between the upper of the footwear and insole region is waterproof in a reliable manner, while permitting any kind of outer soles to be employed.